Split flows across Domains

Tue Jan 24 17:07:34 UTC 2006

"Christopher L. Morrow" <christopher.morrow at verizonbusiness.com> writes:

> On Tue, 24 Jan 2006, Robert E.Seastrom wrote:
>
>>
>>
>> Glen Kent <glen.kent at gmail.com> writes:
>>
>> > For example, an ISP can learn two different equal cost routes to a
>> > foo.com server via two different autonomous domains. It can thus split
>> > different flows (based on src-dest IP, src-dest Port, TOS, etc) across
>> > these two paths.
>> >
>> > Do operators currently do this?
>> >
>> > Folks can send me replies offline in case this constitues a "trade secret"!
>>
>> Works great with a flow-based router (or layer-three-switch-pronounced-
>> 'crippled-router').  The downside, of course, is that you now have a
>> flow-based router in your network, which has been shown to Not Work
>> Well under other specified conditions (worm outbreaks come immediately
>> to mind).
>
> I could be mistaken, but this is also a feature in mbgp, effectively
> loadsharing across two external paths. I presume the paths would have to
> be completely equal all the way down to the router-id and (probably)
> age-of-route ...

He said "via two different autonomous domains", which I took to mean
two upstreams... and my understanding is that (on ciscos anyway)
you're talking per-packet, not per-flow load balancing.

What happens when you intentionally bugger stuff up so that you are
per-packet load balancing your outbound traffic between two diverse
(ie, non-congruent-to-the-same-upstream-and-pop) paths is left as an
exercise to the reader...  but I don't think TCP is gonna like it. :)

                                        ---rob